What matters in installing piping in a nuclear power plant and other large plants is residual tensile stress generated in the inner peripheral surface of the piping. If pipings are connected by welding, for example, residual stress occurs in a weld zone of the pipings. Under this residual stress, stress corrosion cracking (SCC) may occur in the piping, shortening the life of the piping. Thus, it is desirable to reduce the residual stress generated in the piping by welding or the like.
As a residual stress improving apparatus for piping, intended for reducing the residual stress of piping, the apparatus described in Patent Document 1, for example, is known. This apparatus includes an arc generation ring located on the side of the outer periphery of piping, and a ring coil disposed to pinch the ring. If a magnetic field is generated by the ring coil, an arc is produced between the arc generation ring and the piping to heat the piping. Upon heating of the piping, the residual stress of the piping is reduced.
As a residual stress improving apparatus for piping, intended for reducing the residual stress of piping, a high frequency induction heating apparatus or the like is known widely and generally. As a prior art document relevant to the present case, the following Patent Document 1 is available.
Patent Document 1: Japanese Patent Application Laid-Open No. 2001-150178